The genus Thunbergia is made up of about 200 species from warm areas of central and southern
Africa, Madagascar, and Asia. The genus is named after the 18th century Swedish botanist and
explorer, Carl Peter Thunberg. Thunbergia is a twining perennial vine that is often cultivated
for its attractive flowers.
Black-eyed Susan vine is native to tropical eastern Africa, and is widely cultivated and naturalized
in other tropical regions of the world, where it can eventually climb to 20 feet. As an annual in
the colder zones, it will grow from 3-8 feet tall in a single season.
The orange-yellow or white solitary flowers on long peduncles up to 2 inches long, have 5 spreading
petal lobes and dark purple throats. Ovate-triangular toothed green leaves up to 3 inches long.
Blooms in summer to fall, but best bloom is often in late summer and fall after the hot summer
temperatures moderate. They will bloom all year long if night temperatures are above 60° F.
and they get full sun in the winter months.
The plants are not very drought tolerant and should be watered regularly for optimum growth.
Fertilize every other week with a balanced fertilizer diluted to ½ the strength recommended on the
label. Occasional trimming helps keep the plant growing vigorously and helps to promote more blooms.
No serious insect or disease problems. Watch for scale, spider mites and whiteflies on indoor
plants.
Black-eyed Susan vines are cottage garden favorites. They look good in window boxes, mixed containers or
climbing on trellises, arbors, fences or other structures around the home, and as a groundcover.
Also effective in hanging baskets where the vine can twist around the basket supports or in patio
containers with a small trellis.
The vines can grow to five or six feet high if given good support. Clock vines don't bloom
well during high summer heat and humidity, but they will make up for lost time when the weather
cools off, blooming well into October.
Sow seeds indoors 6-8 weeks before the last frost date, for earlier blooms. Cover the seed with
about one fourth inch of growing media. Germination takes 10 to 21 days at 70-75° F., and
seedlings grow very slowly. Wait until the soil has warmed up and night temperatures remain above
50° degrees to transplant outdoors.
Place transplants six inches apart about three inches from a support. Supports will be covered
quickly after the plants become established. Soil should be moist and high in organic matter. Sunny
mornings and afternoon protection are appreciated.
They can be easily grown from seed sewn directly in the garden after last frost date, or may be grown
in containers that can be overwintered indoors in a warm sun room. Plants grown from seed are more
vigorous than those from cuttings.
